Insulin is produced by the beta cells and glucagon by the alpha cells of the Pancreatic Islets of Langerhans. One of insulin's major effects is to lower blood glucose by suppressing hepatic glucose output and stimulating peripheral glucose uptake. Endogenous insulin levels may be low or undetectable in some patients with diabetes mellitus. Exogenous insulin is usually administered to reduce hyperglycemia in situations where circulating insulin levels are either low or ineffective. Glucagon generally has effects opposite to those of insulin, including, primarily, increasing hepatic glucose output and thereby increasing blood glucose levels. Glucagon levels tend to increase when blood glucose levels fall to abnormally low levels, particularly in patients who utilize exogenous insulin.
Current goals for diabetes management include near normal blood glucose levels to delay or prevent microvascular complications; achievement of this goal usually requires intensive insulin therapy. In striving to achieve this goal, physicians have encountered a substantial increase in the frequency and severity of hypoglycemia in their diabetic patients.
Hypoglycemia, characterized by low blood glucose levels, results in autonomic and adrenergic, as well as neuroglycopenic, symptoms; these symptoms typically are encountered as a result of inadvertent excessive insulin administration. Currently, hypoglycemia is defined as a blood glucose of <70 mg/dl, e.g., greater than 50 or 60 mg/dl. Frequent recurrent bouts of hypoglycemia can be associated with hypoglycemic unawareness which can further contribute to development of hypoglycemia which is sometimes severe. Thus, efforts to achieve normal glucose levels with insulin can result in the development of hypoglycemia of varying frequency and severity in patients. Hypoglycemia and the lack of awareness of its presence are serious complications of insulin therapy that occur with greater frequency and severity when impaired counter-regulatory (anti-insulin) responses are present in diabetic patients. One of the major counter-regulatory hormones that normally responds to hypoglycemia is glucagon. Not infrequently, the glucagon response to acute hypoglycemia is impaired or lost in patients with advanced Type 1 and Type 2 diabetes.